Accelerator admixture

ABSTRACT

An accelerator composition for use with sprayed cementitious compositions, which is an aqueous solution or dispersion of a blend of the essential Components 1-3 Component 1—aluminium sulphate Component 2—at least one of an alkanolamine and an alkylene diamine or triamine Component 3—hydrofluoric acid optionally with at least one of Components 4-7, with the proviso that at least one of Component 4 or Component 5 be present: Component 4—at least one of sodium hydroxide, potassium hydroxide, lithium hydroxide, magnesium hydroxide, lithium carbonate, sodium carbonate, potassium carbonate, magnesium carbonate, sodium sulphate, potassium sulphate, magnesium sulphate and lithium sulphate; 
         Component 5—C 1 -C 10  aliphatic mono- and dicarboxylic acids and their metal salts; Component 6—aluminium hydroxide; Component 7—at least one of phosphoric acid and phosphorous acid. The accelerators have excellent long-term stability and work well with “difficult” cements, such as some Japanese OPCs.

This invention relates to low alkali and alkali-free accelerators forsprayed cementitious compositions.

The use in cementitious compositions such as concrete to be applied byspraying of low alkali and alkali-free accelerators in place of thetraditional aluminates and other strongly alkaline materials is now wellestablished. The major components of such accelerators are aluminiumcompounds, the most commonly encountered being aluminium sulphate andamorphous aluminium hydroxide. In addition to these aluminium compounds,a variety of other components have been used in such accelerators, theseincluding alkanolamines, other aluminium salts (such as oxalates andnitrates) and various organic acids. More recent compositions haveinvolved the use of fluoride ions.

The major problem in the art is to find an accelerator composition thatcombines acceptable performance, acceptable stability and an acceptablecompressive strength. Stability can be a problem, especially in the moreextreme conditions sometimes encountered in tunnels, and a reasonableshelf-life is necessary for a practical accelerator. All acceleratorsused in spraying concrete lower the compressive strength compared to thecompressive strength of the same concrete without accelerator. It isnecessary that this lowering be kept to a minimum. In addition, a goodearly strength development in the 1-4 hour period after spraying isparticularly desired.

In addition, the worldwide variation in cement types causes problems.What works well with one cement in, say, Europe will not necessarilywork so well with an Australian or a Japanese cement. It is difficult toformulate an accelerator that will work acceptably well with all types.

It has now been found that a particular combination of materials givesan accelerator that performs especially well and is very stable. Theinvention therefore provides an accelerator composition adapted to beused with sprayed cementitious compositions, which is an aqueoussolution or dispersion of a blend of the essential Components 1-3:

-   -   Component 1—aluminium sulphate    -   Component 2—at least one of an alkanolamine and an alkylene        diamine or triamine    -   Component 3—hydrofluoric acid        optionally with at least one of Components 4-7, with the proviso        that at least one of Component 4 or Component 5 be present;    -   Component 4—at least one of sodium hydroxide, potassium        hydroxide, lithium hydroxide, magnesium hydroxide, lithium        carbonate, sodium carbonate, potassium carbonate, magnesium        carbonate, sodium sulphate, potassium sulphate, magnesium        sulphate and lithium sulphate;    -   Component 5—C₁-C₁₀ aliphatic mono- and dicarboxylic acids and        their metal salts;    -   Component 6—aluminium hydroxide;    -   Component 7—at least one of phosphoric acid and phosphorous acid        the ingredients being present in the following proportions        (active ingredients by weight);    -   Component 1—from 30 to 60%, calculated on the basis of 17%        aluminium sulphate;    -   Component 2—from 0.1 to 15%,    -   Component 3—from 0.2 to 8.0%    -   Component 4—up to 15%    -   Component 5—up to 15%    -   Component 6—up to 15%    -   Component 7—up to 5%.

Component 1, aluminium sulphate, may be any aluminium sulphate used inthe manufacture of accelerators. It may be fully hydrated, or totally orpartially calcined. A typical grade, and the one on which the proportionis based, is “17%” aluminium sulphate (Al₂(SO₄)₃.14.3H₂O) (called thusbecause that is the proportion of aluminium oxide therein). should anyother aluminium sulphate be required, he appropriate quantity can beeasily calculated on this basis. Preferably Component 1 is present inthe proportion of from 30-46% by weight of the total acceleratorcomposition.

Component 2,alkanolamine, alkylene diamine and alkylene triamine may beany such material, but is preferably ethylene diamine, ethylenetriamine, diethanolamine or triethanolamine, most preferablydiethanolamine. It is preferably present in the proportion of from 0.1-10%, more preferably from 0.1 -8%, by weight of the total acceleratorcomposition. It is possible to use a combination of two or more of suchmaterials.

Component 3, hydrofluoric acid is generally used as an aqueous solutionof about 40% HF by weight. The proportion of hydrofluoric acid presentin the total accelerator composition (as HF) is preferably from 2-4% byweight of the total accelerator.

Component 4 may be selected from among the materials previously named.Although sodium and potassium are alkali metals, the proportion of suchmetals in the accelerator compositions according to this invention maybe sufficiently low to permit these accelerators to be considered asalkali-free according to the accepted European definition (lower than 1%(weight) of Na₂O equivalent). Up to 8.5% Na₂O equivalent is considered“low alkali” and is acceptable for many purposes—in many cases, rigorousexclusion of alkali on health and environmental grounds is not necessaryand a small proportion of at least one alkali metal enhances the earlystrength development. Thus, for the purposes of this invention, andcontrary to the current practices of the art with respect to alkali-freeaccelerators, it is preferred that a minor proportion of alkali metal bepresent. This proportion is preferably no higher than 5% Na₂Oequivalent. The preferred proportion of Component 4 is from 1-10% byweight of the total accelerator composition. Component 4 is typicallyadded to the accelerator composition as a 30% weight solution in water.

Component 5 may be selected from one or more of the group of acids.Especially preferred are formic, oxalic and glycolic acids and theirmetal salts, but other acids, such as acetic, propionic, succinic,citric and tartaric acids are also useful. Preferred proportions ofComponent 5 are from 2 -10%, more preferably from 4 -8%, by weight ofthe total accelerator composition.

It is required that at least one of Component 4 and Component 5 bepresent in the composition. The preferred Components 4 and/or 5 for thepurposes of this invention are sodium oxalate, potassium oxalate andmixtures of one or both of these with lithium hydroxide. TheLiOH/sodium-potassium oxalate mixtures are particularly preferred.

Component 6, aluminium hydroxide, is preferably amorphous aluminiumhydroxide of the type normally used in accelerators for sprayedconcrete. It is preferably present in the proportion of up to 10% byweight of the total accelerator composition. It is possible to usecrystalline aluminium hydroxide; this is considerably cheaper, but it isdifficult to dissolve and it does not perform as well as the amorphousmaterial.

Component 7, phosphoric acid (H₃PO₄) or phosphorous acid (H₃PO₃), actsas a stabiliser. Although it is possible to omit it, it confers a usefuldegree of stability on the accelerator compositions of this invention, avital consideration in tunnelling operations where the accelerator mayhave to remain in a ready-to-use state for long periods. It is thereforepreferably present, and in a concentration of from 0.1-2% by weight ofthe accelerator composition. It is possible to use a blend of bothacids, but it is preferred to use phosphoric acid alone.

The accelerator compositions may be prepared by simply mixing theabovementioned components in any order and stirring to give an aqueoussolution. In some cases, additional water will need to be added. Thefinal composition will generally comprise from 40-70% by weight ofwater.

Given the nature of the ingredients, the resulting acceleratorcomposition will not be a simple mixture of ingredients but a complexblend of reaction products. For example, the HF will react with someother components (most especially aluminium hydroxide, if any bepresent). This composition is very stable, having a shelf life undernormal storage conditions of several months.

In use, the accelerator composition of the invention is injected at aspray nozzle in the conventional manner. The dose is typically from 5-12% by weight accelerator composition based on cement weight. Theinvention also provides a method of applying a cementitious compositionto a substrate by spraying, comprising the steps of mixing a batch offluid cementitious composition and conveying it to a spray nozzle, therebeing injected at the nozzle an accelerator as hereinabove described.

Sprayed cementitious compositions that utilise accelerator compositionsaccording to this invention exhibit an unusually rapid build-up ofcompressive strength. In addition, the accelerator compositions workwell with an unusually wide variety of cements, including Japanesecements, with which other alkali-free accelerators give lesssatisfactory results. The invention also provides a hardenedcementitious layer applied to a substrate by spraying through a spraynozzle, there having been added at the nozzle an accelerator ashereinabove described.

The invention is further illustrated by the following non-limitingexamples in which all parts are by weight.

A number of accelerators are added to a test mortar mix having thefollowing constitution: water 198 parts ordinary Portland cement 450parts sand (DIN 196-1) 1350 parts superplasticiser 2.7 parts

The cement is Tayheiyo OPC, a commonly-used Japanese cement. Thesuperplasticiser used is NT-1000 ex NMB Ltd., Japan.

EXAMPLE 1

To the abovementioned mix is added with thorough mixing 31.5 parts of anaccelerator according to the invention and having the followingcomposition (given as percentages by weight): aluminium sulphate (16H₂O)35 diethanolamine 2.1 sodium sulphate 11.2 oxalic acid 7.5 hydrofluoricacid 6 amorphous aluminium hydroxide 9.5 water to 100%

EXAMPLE 2

Example 1 is repeated, with the exception that the 31.5 parts of theaccelerator according to the invention is replaced by acommercially-available alkali-free accelerator sold as MEYCO® SA162.

EXAMPLE 3

Example 1 is repeated, with the exception that the 31.5 parts of theaccelerator according to the invention is replaced by acommercially-available alkali-free accelerator sold as MEYCO® SA170.

The samples are tested for compressive strength according to prEN(preliminary European Standard) 12394 and the results obtained are shownbelow: Compressive strength (MPa) at Example No. 6 h 1 d 7 d 1 3.6 20.139 2 1.4 1.8 23.2 3 0.8 8.6 28.9

It can be seen that the composition comprising the accelerator accordingto the invention develops compressive strength earlier than thecompositions comprising the commercial accelerators, and that the finalstrength is substantially higher.

1. An accelerator composition adapted to be used with sprayedcementitious compositions, comprising an aqueous solution or dispersionof a blend of Components 1-3: Component 1—aluminium sulphate Component2—at least one of an alkanolamine, an alkylene diamine or alkylenetriamine Component 3—hydrofluoric acid Optionally with at least one ofComponents 4-7, with the proviso that at least one of Component 4 orComponent 5 be present: Component 4—at least one of sodium hydroxide,potassium hydroxide. lithium hydroxide, magnesium hydroxide, lithiumcarbonate, sodium carbonate, potassium carbonate, magnesium carbonate,sodium sulphate, potassium sulphate, magnesium sulphate or lithiumsulphate; Component 5—at least one of C₁-C₁₀ aliphatic mono-carboxylicacids, C₁-C₁₀ aliphatic dicarboxylic acids or their metal salts;Component 6—aluminium hydroxide; or Component 7—at least one ofphosphoric acid or phosphorous acid. The components being present in thefollowing proportions (active ingredients by weight); Component 1—from30% to 60%, calculated on the basis of 17% aluminium sulphate; Component2—from 0.1% to 15% Component 3—from 0.2% to 84% Component 4—up to 15%Component 5—up to 15% Component 6—up to 15% Component 7—up to 5%.
 2. Anaccelerator composition according to claim 1, in which Component 4 ispresent.
 3. An accelerator composition according to claim 2, in whichComponent 4 contains alkali metal and is present to the extent that thealkali metal content is a maximum of 8.5% Na₂O equivalent.
 4. A methodof applying a cementitious composition to a substrate by spraying,comprising the steps of mixing a batch of fluid cementitious compositionand conveying it to a spray nozzle, there being injected at the nozzlean accelerator according to claim
 1. 5. A hardened cementitious layerapplied to a substrate by spraying through a spray nozzle, there havingbeen added at the nozzle an accelerator according to claim
 1. 6. Anaccelerator composition according to claim 1, wherein the aluminiumsulphate is at least one of full hydrated, partially calcined or totallycalcined.
 7. An accelerator composition according to claim 1, whereinComponent 2 is at least one of ethylene diamine, ethylene triamine,diethanolamine or triethanolamine.
 8. An accelerator compositionaccording to claim 1, wherein Component 2 is present in an amount offrom 0.1% to 10% by weight of the total accelerator composition.
 9. Anaccelerator composition according to claim 1, wherein hydrofluoric acidis present in an amount of from 2% to 4% by weight of the totalaccelerator composition.
 10. An accelerator composition according toclaim 2, wherein Component 4 contains alkali metal and is present to theextent that the alkali metal content is a maximum of 5% Na₂O equivalent.11. An accelerator composition according to claim 2, wherein Component 4is present in an amount from 1% to 10% by weight of the totalaccelerator composition.
 12. An accelerator composition according toclaim 2, wherein Component 4 comprises a solution in water.
 13. Anaccelerator composition according to claim 1, wherein Component 5 is atleast one of formic acid, oxalic acid, glycolic acid, acetic acid,propionic acid, succinic acid, citric acid, tartaric acid, or metalsalts thereof.
 14. An accelerator composition according to claim 13,wherein Component 5 is at least one of sodium oxalate, potassiumoxalate, or mixtures of one or both with lithium hydroxide.
 15. Anaccelerator composition according to claim 1, wherein Component 5 ispresent in an amount of from 2% to 10% by weight of the totalaccelerator composition.
 16. An accelerator composition according toclaim 1, wherein Component 6 is at least one of amorphous aluminiumhydroxide or crystalline aluminium hydroxide.
 17. An acceleratorcomposition according to claim 1, wherein Component 6 is present in anamount of up to 10% by weight of the total accelerator composition. 18.An accelerator composition according to claim 1, wherein Component 7 ispresent in an amount of from 0.1% to 2% by weight of the totalaccelerator composition.
 19. The method of claim 4 wherein theaccelerator composition is injected in a dose from 5% to 12% by weightof accelerator composition based on cement weight.